For artificially imparting reverberation to a musical tone signal, the most direct method employing an electronic technique is to produce reverberation by superposing signals which have various lengths of time delay relative to the direct sound in accordance with the impulse response in a room in which the reverberation is assumed to occur. According to this method, desired reverberation is produced, as shown in FIG. 1(a), by providing delay signals from a delay memory 1 having plural taps and synthesizing these delay signals by an adder 3 through amplitude adjusters 2-1, 2-2, . . . , 2-n. In the device shown in FIG. 1(a), a reverberation signal is obtained as an output signal Xout which is ##EQU1##
Where X.sub.i represents a signal obtained by delaying an input signal Xin by time .tau..sub.i and g.sub.i represents gains of the respective amplitude adjusters 2-1, 2-2, . . . , 2-n, i.e., values of weighting to the respective delay signals X.sub.i. An echo time pattern of the device of FIG. 1(a) is shown in FIG. 1(b).
In the art of artificially imparting reverberation, it is often practiced, for obtaining as natural reverberation as possible (e.g., reverberation simulating one in a concert hall), to spatially arrange a plurality of reverberation signals to a single input signal (e.g., a musical tone signal of a single musical instrument), i.e., to sound the musical tone signal from a multichannel system such as a two-channel system and a four-channel system. If, however, the two-channel or four-channel system is constructed by simply employing two or four of the devices shown in FIG. 1(a), the size of the device becomes twice or four times as large as the device shown in FIG. 1(a) resulting in a tremendous increase in the manufacturing cost.
There is another problem which concerns a demand for changing the reverberation characteristics depending upon the environment in which the musical tone signal is sounded.
FIG. 2 shows a result of simulation of primary and secondary reflected sounds in a certain actually existing room. There are 11 primary reflected sounds and 24 secondary reflected sounds. If these reflected sounds are simulated by the reverberation imparting device of FIG. 1, a delay memory having 35 taps in all is required. Further, since the respective reflected sounds must be provided with different coefficients, 35 different gain data g.sub.1 to g.sub.35 must be set. This may be tolerable if 35 fixed coefficients only are used. There is, however, a demand for changing reverberation characteristics depending upon the environment such as the size of a concert hall and magnitude of the coefficient of reflection of the wall. If the reverberation characteristics are to be changed specifically according to such specific circumstances, the 35 coefficient parameters g.sub.1 to g.sub.35 must be set again independently. This involves a quite cumbersome operation and therefore is unrealistic.